Gypsum board-forming methods and machines



March 12, 1968 up. GU'TZMAN ET AL 3,373,065

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March 12, 1968 D F. GUTZMAN ET AL 3,373,065

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March 12, 1968 D. F. GUTZMAN ET AL 3,373,065

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612W TOR. BY ZMY7 WfZ/M United States Patent Ofifice 3,373,065- PatentedMar. 12, 1968 3,373,065 GYPSUM BGARD-FORMING METHQDS AND MAfiHINESDouglas F. Gutzman, Arlington Heights, and Rupert J. Straub, Lisle, IlL,assignors to United States Gypsum Company, Chicago, Ill., a corporationof Eliinois Filed Apr. 29, W64, Ser. No. 363,497 18 Claims. ((11. lam-4eABSTRACT 6F THE DESCLUSURE Sealed edge gypsum board of the type havingthe edge portions of the bottom cover sheet underlapping and adhered tothe edge portions of the top cover sheet is formed with the slurry beingconfined entirely by the cover sheets throughout the formation of theboard. Support guides on the support bed of the machine raise the edgeportions of the bottom cover sheet to form a trough which is of a depthsubstantially greater than the clearance in the throat. The slurry isdeposited in this trough. The top cover sheet is guided onto the raisededge portions of the bottom sheet, with these edge portions Contactingthe underside of the top sheet to form an envelope of the cover sheets.Support guides maintain the contact between the cover sheets to confinethe slurry, including the slurry head accumulated at the entrance to thethroat, as the sheets and the slurry are moved to and through the throatand are thereby formed into board.

This invention pertains to methods and machines for forming cementitiousboard, and more particularly to improvements in methods and machines forforming folded edge gypsum board of the type comprising a core of setgypsum plaster covered by top and bottom laminae of fibrous sheets, thebottom sheet extending over the opposite edges of the board and the twosheets overlapping along such opposite edges.

Various methods and machines are known for forming folded edge gypsumboard. Typical machines include a forming table designed to support acontinuous moving web of paper as it is formed into the bottom coversheet of board being produced in the machine. A gang ing element, suchas a master roll, is positioned above the bottom sheet support to definea throat or passageway in which the board is actually formed. Gypsumslurry is deposited on the bottom cover sheet before it passes throughthe passageway beneath the gauging element, and a top cover sheet isapplied in the passageway to encase the gypsum core as it is formed toits boardforming configuration beneath the gauging element.

Previously known machines in common use for forming folded edge boardinclude folder or hopper members at the entrance to the passagewaybeneath the master element. These folders or hopper members confine theslurry at this point, including the head of slurry which is normallyaccumulated at the entrance to the board forming throat. The side edgesof the bottom cover sheet are normally turned upward by folding guides,about scored or kerfed fold lines adapted to form the lower outsidecorners of the board. The outermost edge portions of the bottom sheetare then turned over, beneath the folders, to define the board edges andto provide distal edge strips of the bottom cover sheet on the top sideof the gypsum core where these strips are overlapped by and adhered tothe top cover sheet applied in the boardforming passageway. The foldersare thus normally in contact with the gypsum slurry at the entrance tothe board-forming passageway.

Many efforts have been made toward minimizing or eliminating sticking ofthe slurry to the folders or formers in these machines. However, theseefforts have not been entirely successful. As a result, the slurrycommonly sticks to and is built up on these devices. If this buildup ofslurry is not cleaned off frequently, a large lump forms which willcreate a groove in the formed gypsum core and result in so-calledhollow-edge board. Eventually such a lump will break loose from thefolder and may cause a break in the paper as it passes beneath themaster or forming roll. To avoid this result a machine attendant spendsa good deal of time cleaning the folders.

Further, with these prior art machines and methods, there is acontinuing problem of the slurry or stucco leaking out beneath thefolders, over the inturned edges of the bottom sheet, and interferingwith or preventing the forming of a satisfactory adhesive bond betweenthe overlapped portions of the cover sheets. This is commonly known as astucco edge and results either in a hidden weakness of the paper bondor, if observable, in the rejection of such board as beingunsatisfactory.

The folders of course represent an element of cost of the machine.Further, considerable skill and time are required to obtain propersettings and maintain correct adjustments of the folders forsatisfactory board-forming operation, thereby increasing the cost ofoperation of these prior board-forming machines.

It is an object of this invention to overcome the difficultiesencountered in the forming of folded edge board in the aforedescribedprior machine.

It is another object of this invention to provide improved methods andmachines for forming folded edge gypsum board.

It is another object of this invention. to provide simplified methodsand machines for forming folded edge gypsum board.

It is another object of this invention to provide an improved machinefor forming folded edge gypsum board which eliminates stationary foldingmechanism in contact with the gypsum slurry.

It is another object of this invention to provide improved methods andmachines for forming gypsum board which will insure forming of cleanareas of overlapping contact between the two cover sheets and facilitatethe formation of a good bond therebetween.

In carrying out this invention in one illustrative form, a web of paperwhich is scored along the edges to form the bottom cover sheet of gypsumboard is passed over a support bed and beneath a master forming element.Folding devices are positioned on the entrance side of the form ingelement and spaced apart a distance less than the width of the board tobe formed by the machine whereby the opposite side portions of the webare continuously turned up about lines disposed inward of said web fromthe scored edge lines to form a trough of such bottom cover sheet inwhich a gypsum slurry is deposited. Edge forming guides extend from saidfolding devices to the boardforrning passage beneath the master formingelement in mutually diverging relation, and the trough formed by saidweb is thus permitted to widen to the final board width as it passesfrom said folding devices to said passageway. The side portions of saidweb are simultaneously formed to their board edge defining positions,and a top cover sheet is passed over a guide and into contact with saidside portions above the edge forming guides. The web and top cover sheetconfine the slurry throughout the steps of formation of the boardthereby eliminating any contact of the slurry with stationary machineelements. The support bed is formed with a depressed portion on theentrance side of the master forming element, and includes a ramp whichis inclined upward to said passageway from the depressed portion, topermit the afore-described forming of the paper without undue stretchingor tearing of the edge portions.

For a more complete understanding of this invention reference should nowbe had to the examples illustrated in the drawings wherein:

FIG. 1 is a side elevation view of the board-forming section of amachine employing teachings of this invention;

FIG. 2 is a partial side elevation view of continuous webs of coversheet material, with gypsum slurry being fed therebetween, illustratingthe forming of folded edge gypsum board in the machine of FIG. 1;

FIG. 2a is a cross-sectional view of the bottom cover sheet of FIG. 2taken along line 2a--2a of FIG. 2 and looking in the direction of thearrows;

FIG. 2b is a cross-sectional view of the cover sheets of FIG. 2 takenalong line 2b-2b of FIG. 2 and looking in the direction of the arrows;

FIG. 3 is a perspective view of a portion of the webs as in FIG. 2;

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 of FIG.1 and looking in the direction of the arrows;

FIG. 5 is an enlarged end elevation view of the top guide plate and anedge shim of the machine in E6. 1;

FIG. 6 is a partial cross-sectional view taken along line 6-6 of FIG. 5and looking in the direction of the arrows;

FIG. 7 is a partial perspective view of the bottom side of the guideplate and edge shim of FIG. 5;

FIG. 8 is an enlarged cross-sectional view taken on line 8-8 of FIG. 4and looking in the direction of the arrows, when the machine is inoperation;

FIG. 9 is an enlarged top plan view of one arrangement of the folder andedge guide units for the simultaneous formation of two boards on amachine as in FIG. 1;

FIG. 10 is an enlarged top plan View of one of the folder and guideunits of FIG. 9;

FIG. 11 is an elevation view of the folder and guide unit of FIG. 10;

FIG. 12 is a diagrammatic plan view of a portion of the support bed ofthe machine in FIG. 1, with a paper web thereon for forming a bottomcover sheet;

FIG. 13 is a diagrammatic side elevation view of the bed portion of FIG.12 and including the master roll and top guide plate of the machine inFIG. 1; and

FIGS. l4, 15, 16, 17, 18 and 19 are partial crosssectional views takenalong the correspondingly identified lines in FIG. 13 and looking in thedirection of the respective arrows.

Referring now to the drawings and particularly to FIGS. 1, 4 and 8 theillustrated board-forming machine 20 includes a generally horizontallydisposed bed frame 22 mounted on pedestals 24- and supporting a formingtable 26, generally as in a conventional machine of this type. The table26 is adapted to support a web of material to be moved thereover, fromright to left in FIG. 1, for forming the bottom lamina of folded edgeboard. A first table section 28 extends horizontally at the webreceiving end of the machine and is coplanar with a board supportsection 30 which receives and supports wet board that is formed beneatha master roll 32 disposed above the receiving end of section 30 asillustrated. The remainder of table 26 and related mechanism, betweensections 23 and 30, serves to form the bottom lamina or cover sheet fromthe moving web in accordance with teachings of this invention, to bemore fully described below.

The illustrated master roll and the receiving end of section 30 definethe upper and lower limits of the throat or passageway in which theboard is formed. The master roll is vertically adjustably mounted topermit selectively varying the clearance in the passageway therebeneathand hence to provide control of the board thickness in a known manner.For instance, the illustrated roll 32 is mounted on arms 34 supported onbeams 36 pivotally mounted on the bed frame at one end (not shown) andhaving the opposite end 36a supported by adjustable support members 38and 4t). A selectively adjustable support 38 is provided for each beam36 and may comprise a jack screw driven by a motor through a reductiongear (not shown) to permit accurate control of the board thickness.Support 49 engages a beam 42 extending beneath beam 36 and may comprisea hydraulic cylinder jack for emergency raising of the master roll 32.Other means of adjustably supporting a master roll or other masterelements are known in the art.

With reference to FIG. 4, a link 44 is pivotally joined to one beam 3t;and to a bed frame member at the opposite side of the machine tolaterally stabilize the support frame on which the master rolll ismounted.

Referring now to FIGS. 1, 2 and 3, in the general operation of theillustrated type of machine a paper web 46 for forming a bottom laminais passed over table 26 and beneath master roll 32. Scoring wheels or,usually, kerfing wheels 48 are placed to form pairs of spaced parallelfold lines 50 and 52 spaced inward of the opposite edges of the web. Theportions 54- of the web between the score lines are adapted to cover theedges of the board, and the edge strips 56, outward of the outer edgescore lines 50, normally underlap a top cover sheet. A gypsum slurry isdeposited on web 46 from supply means such as a pipe or pipes 58. Theslurry accumulates in a pile or head at the entrance to the passagewaybeneath roller 32 where it spreads out and is metered by the masterelement 32.

Referring now more particularly to FIGS. 2, 2a, 2b and 3, whichillustrate the novel and improved method of the present invention aspracticed with the machine of FIG. 1, the two lateral edge portions ofthe web are progressively raised and turned upward about lines disposedinwardly of the edge score lines 52 to form a trough of the web, on theentrance side of the board-forming passageway. A portion of this troughadjacent the passageway, is of a width somewhat less than the width ofthe board to be formed and of a depth substantially greater than thecombined width of strips 54 and 56 (see FIGS. 2 and 2a). This isobtained by raising the edge portions of the web and turning the edgeportions, including portions 54 and 56, to a vertical position aboutlines disposed inwardly of score lines 52 (see FIG. 2a). Thus, at itsdeepest point, a short distance upstream from roll 32, the illustratedbottom web forms a trough as seen in FIG. 2a, including a generallyfiat, horizontal center portion, opposite portions, both inwardly of therespective portions 54, extending outward and upward from the centerportion, and edge portions comprising strips 54 and 56 and contiguousportions of the web extending upward from fold lines inward of lines 52.In vertical depth, this trough extends both above and below the edgeportions 54 to provide a deep trough with minimum stretching of the web.From the area of maximum depth of the trough to the nip of roll 32, theedge portions 54 are supported in vertical positions but in mutuallydiverging relation, and the edge portions 56 are turned in (see FIG. 2b)to pass beneath the roll in generally horizontal positions so that thetrough widens and collapses to the width and thickness of the board tobe formed as the web approaches and passes through the passagewaybeneath the master element (see FIG. 3).

The gypsum slurry is deposited in the trough as illustrated. Due to thedepth of the trough, i.e. the height of the upwardly extending lateraledge portions of the web, the head of slurry which accumulates at theentrance to the board-forming passageway is laterally confined by thelower web 46. A web 60 for forming the top cover sheet is brought intocontact with the upstanding edge portions 56 of web 46 approximately atthe deepest part of the trough and maintained in contact with these edgeportions during the widening and collapse of the trough to the finalboard dimensions whereby the slurry is entirely confined by the two websof fibrous material during the board-forming process. Web 60 is adheredto the horizontal edge portions 56 beneath the master element 32 so thata board of the selected width and thickness is formed.

It has been found that the outermost edges of underlap portions 56remain in contact with the cover sheet from initial contact throughoutthe folding process. This insures containment of the slurry andprovision of a clean bonding surface on portions 56 in parallelface-to-face Contact with the cover 60 to effect a good bond between thecover sheets.

With further reference now to FIGS. 1 and 12, the machine 20 is adaptedto carry out the abovedescribed process, and includes a depressedsection in the table 26 on the entrance side of the master roll 28. Thisdepressed section includes a declining section 62 which extends from thefirst section 28 downward to a bottom horizontal section 64. A shortinclined ramp section 66 extends from the lower section 64 up to thelevel of the adjacent end of the board support section 30 at the nip ofmaster roll 32. Edge supports and folding guides for the lower web areprovided along sections 62, 64 and 66 to insure uniform and positivecontrol of this web as it pro gresses through the machine 20.

Referring particularly to FIGS. 4 and 9-11, suitable folding guides 68aand 6% are positioned over the end of section 64 adjacent the lower endof ramp 6 6. The folding guides 68 are mounted on support brackets 70and 71 depending from a transverse bar 72 supported on the bed frame 22.The guides are parallel to the longitudinal axis of bed 26, and arearranged in opposed pairs, one pair 68a-63b being used for each boardbeing formed in the machine 20. The two guides of each pair are spacedapart a distance X (FIG. 9) which is somewhat less than the width Y ofthe board to be formed whereby the opposite edge portions of the bottomweb passing therebetween are folded upward about lines disposed inwardof the web &6 from the edge score lines. A support wedge or shim 74 isprovided along the lower edge of each guide 68, see also FiG. 18. Thesewedges extend diagonally across the corners between section 66 and therespective guides 68 to support corresponding opposite portions of theweb -46, inward of the edge portions 54, as the web moves between a pairof guides 68.

Edge guides 76a and 76b extend from the respective folding guides 68 upthe ramp 66, the edge guides of each opposed pair 76a76b extending indiverging relation. Each edge guide 76 carries an edge former 78 at itsdistal end; the edge formers being disposed directly beneath master roll28 in the board-forming passageway. The edge formers extend generallyparallel to the direction of travel of the web 46, and the formers oneach pair of guides are spaced apart a distance Y (FIG. 9) equal to thewidth of the board to be formed. Each edge guide 76 forms a smoothjuncture with the inner surface of the respective folding guide 68 andis tapered at its distal end to effect a smooth juncture with the innersurface of the respective edge former 78. A tapered support wedge orshim '80 is provided along the lower edge of each guide 76in the samegeneral manner as wedges 74 on guides 68, see also FIG. 19. Each wedge80 conforms generally to the respective Wedge 74 at its inner end andtapers to a point at the outer end of the respective guide 76 asillustrated. Referring particularly to FIGS. 9 and 10, the edge guides76 are pivotally joined to the folding guides as on pins 82 and arespring-biased to their outward or diverging position as by torsionsprings 84. A stop bar 86 is welded to each edge guide 76 and extendsrearwardly therefrom adjacent the respective folding guide. A thumbscrew 88 extends through the distal end of the bar 86 and engages therespective folding guide whereby the angularity and thus the position ofeach edge guide may be varied.

: Clips 90 may also beprovided on folding guides 68 to engage over therespective edges of web 46, see FIG. 18. Such clips will insure that theweb edges remain upright and spread open, against guides 68, as thebottom web is drawn through machine 20. Guide fingers 92 may also beprovided on the edge guides 76. These fingers extend upward and inwardof guides 76 (see FIG. 19), t insure that edges 56 fold inward of theweb as the web proceeds from the fully formed and open trough positionbetween guides 68 to the collapsed board-forming position in the throatbeneath the master element 32.

With particular reference now to FIGS. 12-17, wedgeshaped supports orshims 94 and 96 progressively lift and form the edge portions of the web46 to provide a smooth transition of the Web from its original flatstate to the trough position between guides 68. Each support 94comprises an elongated, inverted right-angular member including asupport surface or ram-p 94a extending beneath the path of travel of therespective edge portion of a web 46 in convergent reiation to the centeraxis of the web, whereby the edge of the web is caused to ride upgradually on the supporting surface @441, see FIGS. 12, 14 and 15. Eachsupport 96 also comprises an elongated, inverted right-angular member,and extends between a support 94' and the respective guide 68,substantially parallel to the direction of movement of the web 46. Thesupport surface or ramp 96a conforms to the adjacent end of ramp 94a andto the adjacent end of the: respective wedge 74. it will be noted,particularly from FIG. 12, that each guide 68 is disposed inward of thehigh point or peak of the respective support surface 9 69. A verticalfol-ding bar 98 is positioned atop each surface 96a and extends from thehigh point of the surface 96a, at the upstream end adjacent support 94,to a position conforming to the ad jacent end of the respective guide 68:at the downstream end as illustrated, see FIGS. 12, 13, 16 and 17. Thisprovides a gradual transitional guide for folding the outer edges of theweb to their vertical position for passage between guides 68 asaforedescri'bed.

Referring now to FIGS. 1, and 4-8, an arcuate guide 100 for the topcover sheet web 6t) is positioned above the outer end of ramp 66 and isadjustably supported on arms 34 as by suitable mounting brackets 102. Atop guide plate 1&4 is supported on brackets 102 with arcuate guide 160and extends from the lower edge of guide 100 to the throat beneath roll32. The guides 100 and 104 extend the full length of the master roll(FIG. 4), or at least the full width of the top web 60. The lowersurface of plate 104 defines a plane including the lower edge of guide100 :and tangent to the master roll 32 at the throat, this plane beingat an angle to the horizontal which is approximately equal but oppositeto the angle by which ramp 66 is inclined to the horizontal. The edge ofplate 184 beneath roll 32 may be tapered, as at 104a.

.Edge shims 1% are provided at each end of plate 104 as illustrated inFIGS. 5-7. These shims are designed to bring the edge portions of thetop and bottom cover sheets into early and firm engagement over ramp 66to prevent leakage of the slurry between the edges of these sheets asthey converge toward the nip or board-forming throat beneath roll 32.Each shim 106 is wedge-shaped or triangular in cross section, takenlateral to the direction of movement of the webs, and presents itsdeepest area along the respective edge of plate 104. The shims 106 arealso triangular in longitudinal cross section, and each includes a camor ramp surface 1416a which rises rather abruptly to a smoothly rounded:apex 10612, and a longer, more shallowly inclined rear surface 1060. Asupport bracket 108 is provided beneath the apex, and an adjustablesecuring device such as a deep C-clamp 110 is provided for adjustablysecuring each shim to plate 104. The shims may thus be selectivelypositioned laterally of the webs to provide preselected effective depthsof the shims between the edges of the web 60 and the plate 104.

Suitable paste applicators 112 (FIGS. 1 and 8) are positioned adjacentroll 32 to apply paste or other adhesives to web 60 along the edge areasthereof which ultimately overlap the edge portions 56. After the edgeportions 56 are turned inward 'by the guides as aforedescribed, they arecontacted by the adhesive carrying edges of top web 60. An adhesive bondis then effected between the top and bottom cover sheets of the finishedboard when web 6% is pressed down upon the inturned strips 56 by themaster roll 32.

in the machine 26, the dimension by which any given portion of bedsections 62, 64 and 66 is depressed below the plane of sections 23 and3t) approximates the vertical displacement of the central portion of web46 from edge portions 54 at a corresponding point in forming the webtrough. For instance section 64 is spaced beneath the plane of sections28 and 30 by a dimension approximating the sum of the vertical rise ofthe web 46 on supports 96 and the height of portions 54 on the foldingbar 98 at any cross section therethrough. As :a result, edge portions 54extend approximately horizontally through the machine, note FIG. 2. Thisconstruction minimizes the tensioning and stretching of the upwardlyfolded distal edges 56 and thereby minimizes the risk of tearing of theweb 46, or of wrinkling, which otherwise would be attributable to thevertical displacement of the edges rela tive to the center portion ofthe web.

Referring particularly to FIG. 8, it will be observed that the head orpile-up of slurry which tends to occur at the entrance to theboard-forming passageway is illustrated as distributed from the nip ofmaster roll 32 back along guides 76 and, to some extent, along guides68. The operator normally observes this head as the prime indicator ofwhether adequate slurry is being supplied to the machine 2i; andproperly distributed to form satisfactory board. For this reason hefeeds adequate slurry to obtain formation of the head a sutficientdistance upstream from the throat to insure ready visibility. Withmachine 2%, and the described method, the slurry head is confined withinthe paper webs at all points and does not contact any stationarymechanism of the board-forming machine. Also, the outer surfaces ofstrips 56 are not exposed to the slurry and little or no opportunity isafforded for slurry to leak out of the web envelope and into contactwith these edges, thereby avoiding stucco edges and insuring good bondsbetween the two cover sheets.

In one specific embodiment of a machine according to the illustrationherein, the receiving section 28 and the board support section 39 weredisposed horizontally and in coplanar relationship. The bottom tablesection 64 was 4 long and depressed 1 /2" below the level of the section30. The declining section 62. was 8 long, whereas the ramp 66 was 12%"long and was disposed at an angle of about 7 to the horizontal. Thismachine was arranged for forming two 2' wide boards /2 thick. Thedimension between the respective folding guides 68a and 68b was 1'11"and the dimension between the respective edge formers, was 2', with theedge guides 74 extending therebetween as illustrated in FIG. 9. Supports74 were 1%" high at the guides 68, and 2%" wide as seen in FIG. 18. Theremaining supports and fold bars were dimensioned and positionedaccordingly as described above and illustrated in the drawings. Arcuateguide 100 was formed with a radius of curvature of 6" and was positionedabove the outer end of ramp 66 as illustrated in FIG. 8. Plate 104 was 9long and extended from the lower edge of the guide along a plane tangentto master roll 32 at the board-forming passageway, and defined an angleof about 7 to the horizontal. Each shim 106 was about 8" in maximumwidth (as seen in FIG. K1 in maximum depth at the apex, which was about2" back of the leading corner, and about 5" in length (lateral to thedirection of web movement). Surface 1060 was thus at an angle of about 7to the plate 1, or horizontal, with surface idea at an angle of about 20to plate 194 or 27 to the horizontal.

It will be obvious that certain other modifications of the specificembodiment shown and described may be made by those skilled in this artwithout departing from the spirit and scope of this invention. Forinstance, the entire receiving end of the table may be coplanar with thelower table section 64, thereby eliminating the declining section 62.Also, various master elements, such as stationary arcuate plates may besubstituted for the master roll 32, various support bed elements such asrollers or conveyors may be substituted, edge formers of variousconfigurations may be utilized, such as for forming tongue and grooveboard, and various support arrangements may be substituted forsupporting the master element. Various folding and forming guides andsupports may be utilized to control the movement and forming of the websand, in some instances, part or all of the supports or shims, clips andfingers may be eliminated, depending to a substantial degree upon thecondition and uniformity of the web product and particularly its edgeportions.

The method of this invention, in its broader aspects, can be carried outwith other machines than that disclosed, as has been noted above, andmay be carried out on machines having conventional fiat web supportingbeds provided due care is exercised in folding and manipulating the edgeportions of the sheet, though the risk of tearing of the edge portionswould be significantly increased thereby.

It will be seen that an improved method and an improved machine forforming folded edge gypsum board have been provided. In following theteachings of this invention, the slurry is entirely confined within thefibrous webs forming the top and bottom cover sheets whereby contactbetween stationary folding mechanism and the gypsum slurry iseliminated. Further, the slurry is confined within the fibrous sheets ina manner to prevent contacting of the overlapping edges of the sheet bythe slurry whereby the risks of obtaining stucco edges are greatlyreduced or eliminated. The overlapping sheet portions are positionedparallel, and in full face-to-face contact to permit formation of asatisfactory bond with minimum overlap, thus permitting use of narrowerpaperwebs. These results can be obtained by relatively inexpensiverebuilding of previously used machines. In addition, the disclosedimprovements in board-forming rnachines provide an advantageousarrangement for practicing the novel method set forth herein.

While a particular embodiment of this invention is shown, it will beunderstood, of course, that the invention is not to be limited theretosince many modifications may be made by those skilled in this art,particularly in light of the teachings provided by the applicants. It iscontemplated therefore by the appended claims to cover any suchmodifications as come within the true spirit and scope of thisinvention.

We claim:

1. A method of forming folded edge board including a core, which isformed from a slurry, a bottom cover sheet which extends over the bottomof said core and includes side portions extending over the side edgesand the marginal portions of the top of said core, and a top cover sheetwhich extends over the top of said core and overlaps said bottom sheetover said top marginal portions, comprising the steps of moving anelongated bottom cover sheet generally horizontally through aboard-forming throat, continuously elevating opposite marginal portionsof said bottom sheet with respect to the center portion of said bottomsheet, in an area upstream from said throat, to form a trough thereofhaving a depth greater than the thickness of the board to be formed insuch throat, depositing such slurry in said trough, advancing a topcover sheet over said trough .and onto the elevated marginal portions ofsaid bottom cover sheet, upstream from said throat, to form an envelopeof said cover sheets which is of a depth greater than the thickness ofthe board to be formed in said throat, collapsing said envelope andforming said cover sheets and slurry to the desired crosssectionalconfiguration for such board while advancing said cover sheets from thearea of initial contact therebetween to and through said throat, andmaintaining con tact between said marginal portions of said bottom coversheet and the underside of said top cover sheet during such advancement,thereby confining'said slurry within said sheets as said sheets andslurry are formed into such board.

2. A method as in claim 1 wherein said side portions are turned upwardto generally vertical positions in forming said trough.

3. A method as in claim 2 wherein said side portions are turned upwardabout lines disposed inward of the respective side portions.

4. A method as in claim 1 wherein said step of elevating oppositemarginal portions of said bottom sheet to form said trough comprisesraising said side portions and adjacent portions of said bottom coversheet with respect to the center portion of said bottom cover sheet.

5. A method as in claim 4 wherein said side portions are turned upwardwith respect to said adjacent portions.

6. A method as in claim 1 wherein, when said top sheet is advanced ontosaid elevated marginal portions, each of such marginal portions contactssaid top cover sheet inward of the respective edge of said top coversheet.

7. A method as in claim 1 wherein each of the outermost edges of saidbottom cover sheet contacts said top cover sheet inward of therespective edge of said top cover sheet throughout such contact betweensaid sheets, and said sheets are subsequently bonded to one another inthe areas outward of such contacts.

8. A method as in claim 1 wherein said center portion of said bottomsheet is formed downward, with respect to a horizontal plane throughsaid throat, in forming said trough.

9. A method as in claim 8 wherein the portions of said bottom sheet forcovering said side edges are moved substantially horizontally informingsuch board.

10. A method as in claim 1 wherein said slurry is a gypsum slurry andsaid cover sheets are webs of paper.

11. A machine for forming board having a core encased by bottom and toplaminae of fibrous material comprising a generally horizontally disposedsupport bed over which a continuous bottom lamina is moved as a slurryof core material is deposited thereon and such slurry and laminae areformed into board, an upper forming element positioned above said bedand defining a passageway therewith for forming such board, saidpassageway having an entrance and exit, spaced supports over said bed onthe entrance side of said passageway for elevating and supportingopposite marginal portions of such lamina to form a trough of suchbottom lamina for receiving such slurry,

a top lamina guide disposed over said bed and spaced from saidpassageway on the entrance side thereof, said guide being positioned toguide a continuous top lamina onto the elevated marginal portions of abottom lamina supported by said spaced supports, and further supportsextending from said spaced supports and from said guide to saidpassageway and disposed to support said laminae and maintain contacttherebetween to confine such slurry therein as such laminae and slurryare moved to said passageway and formed into board.

12. A machine as in claim 11 wherein each of said spaced supportsincludes a wedge-shaped element for raising a marginal portion of suchbottom lamina.

13. A machine as in claim 12 wherein each of said spaced supportsincludes a side folder for turning a marginal portion of such bottomlamina upward, said side folders being in opposed relation to oneanother and spaced apart a distance less than the width of the board tobe formed in such machine.

14. A machine as in claim 11 wherein said top lamina guide includes anelongated arcuate guide member disposed above said spaced supports, anda guide plate extending from said arcuate guide to said passageway.

15. A machine as in claim 14 wherein the lower edge of said top laminaguide, over said spaced supports, is disposed above a horizontal planethrough the top of said passageway.

16. A machine as in claim shaped element at each edge of said plate forurging the marginal portions of such top lamina downward.

17. A machine as in claim 11 including a guide element associated witheach of said spaced supports and disposed to turn the respective distaledge portion of such bottom lamina inward.

18. A machine as in claim 11 wherein said support bed includes a bottomsection disposed below a horizontal plane through the bottom of saidpassageway, and a ramp section extending from said bottom section upwardto said passageway, said spaced supports being disposed over said bottomsection.

14 and including a wedge- References Cited UNITED STATES PATENTS Re.16,860 l/1928 Armstrong 15640 1,383,255 6/1921 Birdsey 156348 1,428,8279/1922 Brookby 156-40 1,750,621 3/1930 A Brookby 156-347 1,790,2521/1931 Speer 156-40 1,824,420 9/1931 Absmeier 156-348 2,722,262 11/1955Eaton et al. 156-348 MORRIS SUSSMAN, Primary Examiner.

